1 .
设等比数列
的前
项的和为
,公比为
.
(1)若
成等差数列,求证:
成等差数列;
(2)若
(
为互不相等的正整数)成等差数列,试问数列
中是否存在不同的三项成等差数列?若存在,写出两组这三项;若不存在,请说明理由;
(3)若
为大于
的正整数.试问
中是否存在一项
,使得
恰好可以表示为该数列中连续两项的和?请说明理由.
设等比数列
![](https://img.xkw.com/dksih/QBM/2015/12/7/1572344066768896/1572344072904704/STEM/352e4ea25cf94daa99022e56d732ebdd.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b6a24198bd04c29321ae5dc5a28fe421.png)
![](https://img.xkw.com/dksih/QBM/2015/12/7/1572344066768896/1572344072904704/STEM/2484acd30a8d402db42bdbc8681c795c.png)
![](https://img.xkw.com/dksih/QBM/2015/12/7/1572344066768896/1572344072904704/STEM/23ea45124f504117bf90d8fefbc84fb7.png)
(1)若
![](https://img.xkw.com/dksih/QBM/2015/12/7/1572344066768896/1572344072904704/STEM/80c2b81604534c81a787b04c5595033c.png)
![](https://img.xkw.com/dksih/QBM/2015/12/7/1572344066768896/1572344072904704/STEM/60ac867a20ac40f39c7726823aec9478.png)
(2)若
![](https://img.xkw.com/dksih/QBM/2015/12/7/1572344066768896/1572344072904704/STEM/4bb2c112f96b48a58907216f66ff3068.png)
![](https://img.xkw.com/dksih/QBM/2015/12/7/1572344066768896/1572344072904704/STEM/8ba9b1338987472487b70a087d714edf.png)
![](https://img.xkw.com/dksih/QBM/2015/12/7/1572344066768896/1572344072904704/STEM/352e4ea25cf94daa99022e56d732ebdd.png)
(3)若
![](https://img.xkw.com/dksih/QBM/2015/12/7/1572344066768896/1572344072904704/STEM/0784519653594ec282f8fd5af1a4c72b.png)
![](https://img.xkw.com/dksih/QBM/2015/12/7/1572344066768896/1572344072904704/STEM/043c237f4731451c87e9d0548647801e.png)
![](https://img.xkw.com/dksih/QBM/2015/12/7/1572344066768896/1572344072904704/STEM/352e4ea25cf94daa99022e56d732ebdd.png)
![](https://img.xkw.com/dksih/QBM/2015/12/7/1572344066768896/1572344072904704/STEM/2aa146f1bfc549e5a6846940651b335d.png)
![](https://img.xkw.com/dksih/QBM/2015/12/7/1572344066768896/1572344072904704/STEM/2aa146f1bfc549e5a6846940651b335d.png)
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12-13高三上·上海徐汇·期中
2 . (1)等比数列{
}中,对任意
, n∈N时都有
,
成等差,求公比q的值
(2)设Sn是等比数列{an}的前n项和,当S3,S9,S6成等差时,是否有a2,a8,a5一定也成等差数列?说明理由;
(3)设等比数列{an}的公比为q,前n项和为Sn,是否存在正整数k,使Sm﹣k,Sm+k,Sm成等差且an﹣k,an+k,an也成等差,若存在,求出k与q满足的关系;若不存在,请说明理由.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0bfccafa83afe5ee21eab6ef2b2c8852.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/6d0b888fa462e7d2bcb8f4614b9d5ac5.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/fd4b498ec6006fb3a5cabf6632c1e355.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d8531dd06d3201ecd71af0cb6a516098.png)
(2)设Sn是等比数列{an}的前n项和,当S3,S9,S6成等差时,是否有a2,a8,a5一定也成等差数列?说明理由;
(3)设等比数列{an}的公比为q,前n项和为Sn,是否存在正整数k,使Sm﹣k,Sm+k,Sm成等差且an﹣k,an+k,an也成等差,若存在,求出k与q满足的关系;若不存在,请说明理由.
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3 . 已知数列
满足![](https://img.xkw.com/dksih/QBM/2015/3/27/1572041501442048/1572041507430400/STEM/a45b3781bb2c47ffaee6fd7ce9f1a28b.png)
(1)设
是公差为
的等差数列.当
时,求
的值;
(2)设
求正整数
使得一切
均有![](https://img.xkw.com/dksih/QBM/2015/3/27/1572041501442048/1572041507430400/STEM/1140e4a27a464392be74aaaa9274b674.png)
(3)设
当
时,求数列
的通项公式.
![](https://img.xkw.com/dksih/QBM/2015/3/27/1572041501442048/1572041507430400/STEM/dfa0f9414ccd4f68b4eb5027024828cf.png)
![](https://img.xkw.com/dksih/QBM/2015/3/27/1572041501442048/1572041507430400/STEM/a45b3781bb2c47ffaee6fd7ce9f1a28b.png)
(1)设
![](https://img.xkw.com/dksih/QBM/2015/3/27/1572041501442048/1572041507430400/STEM/e82efafd7d1449c9a4d3d11fddd4d99a.png)
![](https://img.xkw.com/dksih/QBM/2015/3/27/1572041501442048/1572041507430400/STEM/c1085bcc0bd74ef7b0073ed24cf01b04.png)
![](https://img.xkw.com/dksih/QBM/2015/3/27/1572041501442048/1572041507430400/STEM/6201dbdb6ce5493fbf728813f3105ab4.png)
![](https://img.xkw.com/dksih/QBM/2015/3/27/1572041501442048/1572041507430400/STEM/8032c35a4555485dbf357264f097eb6b.png)
(2)设
![](https://img.xkw.com/dksih/QBM/2015/3/27/1572041501442048/1572041507430400/STEM/23d8e35a55e14431be6ac98961f6c237.png)
![](https://img.xkw.com/dksih/QBM/2015/3/27/1572041501442048/1572041507430400/STEM/44ce5aec71ae420e8218f9cc34b42a53.png)
![](https://img.xkw.com/dksih/QBM/2015/3/27/1572041501442048/1572041507430400/STEM/3a7586f2ab3147ddb518802b5c91974f.png)
![](https://img.xkw.com/dksih/QBM/2015/3/27/1572041501442048/1572041507430400/STEM/1140e4a27a464392be74aaaa9274b674.png)
(3)设
![](https://img.xkw.com/dksih/QBM/2015/3/27/1572041501442048/1572041507430400/STEM/62691231266d4075b4de28883021ddec.png)
![](https://img.xkw.com/dksih/QBM/2015/3/27/1572041501442048/1572041507430400/STEM/6201dbdb6ce5493fbf728813f3105ab4.png)
![](https://img.xkw.com/dksih/QBM/2015/3/27/1572041501442048/1572041507430400/STEM/5e6f735911164bac933a260ec479baa3.png)
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